Linear compressor

ABSTRACT

In a linear compressor having a compression mechanism for compressing and discharging a refrigerant, an inflammable refrigerant or a natural refrigerant such as propane, isobutane, carbon dioxide or the like is used as the refrigerant while no lubricating oil is filled up, thereby improving the system efficiency and reducing the amount of refrigerant.

TECHNICAL FIELD

The present invention relates to a linear compressor (vibration typecompressor) for use in a refrigerator-freezer, an air conditioner or thelike.

BACKGROUND ART

A refrigerant CFC-12 (dichlorodifluoromethane, CCI₂F₂) or HCFC-22monochlorodifluoromethane, CHCIF₂) has been primarily utilized inconventional compressors for use in a refrigerating cycle or the like.However, in view of the influence of ozone layer damage on the humanbody or other living things or on the global warming, an HFC-basedrefrigerant containing no chlorine (CI) atoms in a molecule, such asHFC-134 a (1,1,1,2-tetrafluoroethane, CH₂FCF₃), has come to be used.

In recent years, as disclosed in Japanese Laid-open Patent PublicationNo. 8-200224, an inflammable refrigerant such as propane or isobutane ora natural refrigerant is gradually utilized in reciprocatingcompressors, rotary compressors, scroll compressors or helical bladecompressors.

As compressors other than those referred to above, Japanese Laid-openUtility Model Publication No. 58-116784 discloses a linear compressor.

A conventional linear compressor is explained hereinafter with referenceto the drawings.

FIG. 6 depicts a conventional linear compressor having a compressionmechanism 1 that includes a motor 3, a cylinder 5, a bearing 6, a piston8, a cylinder head 10 and a resonant spring 11, and is elasticallysupported by suspension springs (not shown) within a closed casing 2.The motor 3 includes a stationary element 4 and a movable element 7secured to the piston 8.

The cylinder 5 and the bearing 6 axially movably support the piston 8.The resonant spring 11 has one end secured to the movable element 7 ofthe motor 3 and the other end secured to the bearing 6, and a portionthereof is submerged under lubricating oil 12 stored within the closedcasing 2. 8 a denotes a compression chamber defined by the cylinder 5and the piston 8. A refrigerant gas introduced into the compressionchamber 8 a through a suction hole 8 b in the piston 8 is compressed viaa reciprocating motion of the piston 8.

The lubricating oil 12 stored at a lower portion within the closedcasing 2 is stirred by expansion and contraction of the resonant spring11 following the axial reciprocating motion of the piston 8. Thelubricating oil 12 then scatters within the closed casing 2 to lubricatethe sliding portions between the piston 8 and the cylinder 5, and thesliding portions between the piston 8 and the bearing 6.

The refrigerant used is CFC-12 or HCFC-22 that has been hitherto usedprimarily in a cooling system, while mineral oil is primarily used forthe lubricating oil 12.

Cast iron or an aluminum-based alloy is used for the sliding membersconstituting the sliding portions such as the cylinder 5, piston 8,bearing 6 and the like. In some cases, surface treatment such asmanganese phosphate-based chemical conversion coating is appliedthereto.

However, the lubricating oil 12 is used in the conventional linearcompressors, and some lubricating oil is used in the compressors such asthe reciprocating compressors, rotary compressors, scroll compressors orhelical blade compressors, in which a natural refrigerant or aninflammable refrigerant is used. The use of the lubricating oil 12lowers the heat exchanging efficiency in the cooling system, thus givingrise to the possibility of lowering the efficiency of the coolingsystem.

By way of example, considering the case where the aforementionedrefrigerant is used in the compressors, for example, the conventionallinear compressors, in which an inflammable refrigerant or naturalrefrigerant such as propane, isobutane, carbon dioxide or the like isused, the inflammable refrigerant or natural refrigerant dissolves inthe lubricating oil 12 within the compressors. In particular,hydrocarbons dissolve in the lubricating oil 12 in larger amount thanother refrigerants. Because of this, the amount of refrigerant requiredfor the cooling system must be increased by the amount that dissolves inthe lubricating oil, compared with the cooling system in which nolubricating oil is used. In particular, when hydrocarbons are used, ithas been considered that the amount of refrigerant must be furtherincreased.

The use of an increased amount of the natural refrigerant or inflammablerefrigerant results in an increase in cost, and if the refrigerantleaks, there is a possibility of catching fire or explosion.

Furthermore, because the compression mechanism 1 is arrangedhorizontally in the conventional linear compressors, a lateral load isapplied to the sliding portions between the piston 8 and the cylinder 5and between the piston 8 and the bearing 6 by the weight of the piston8, the movable element 7 of the motor 3 and the like. This increases thesliding loss, and if no lubricating oil is used, there is a good chancethat the sliding portions may be subjected to wear or seizing.

The present invention has been developed to overcome the above-describeddisadvantages.

It is accordingly an objective of the present invention to provide aninexpensive, safe and highly reliable linear compressor capable ofreducing the amount of refrigerant for use in the cooling system,improving the heat exchanging efficiency in the cooling system, and alsoimproving the efficiency of the whole cooling system.

DISCLOSURE OF THE INVENTION

In accomplishing the above objective, the linear compressor according tothe present invention is characterized by including a closed casing anda compression mechanism arranged vertically within the closed casing forcompressing and discharging a refrigerant, wherein an inflammablerefrigerant or a natural refrigerant is used as the refrigerant while nolubricating oil is filled up.

According to the above-described construction, because no lubricatingoil is used, the heat exchanging efficiency in a cooling system isimproved and the efficiency of the whole cooling system is improved.Furthermore, because the refrigerant does not dissolve in thelubricating oil, the amount of refrigerant to be used in the coolingsystem is reduced, and the cost is also reduced. Even if the refrigerantleaks, the possibility of catching fire or exploding is reduced,enhancing the safety.

The use of propane, isobutane or carbon dioxide for the refrigerant doesnot cause any problem associated with ozone layer damage, thus enhancingthe safety.

If a sliding surface in the compression mechanism is surface-treatedwith Teflon TM (polytetrafluoroethylene), molybdenum disulfide andalumite, the self-lubricating effect of a surface-treating agentprevents abnormal wear at the sliding portion of a piston and a cylindereven without any lubricating oil, thus enhancing the reliability. Also,the surface treatment reduces the coefficient of friction on the slidingportion and reduces the sliding loss, thus enhancing the compressorefficiency.

In another aspect of the present invention, a linear compressor ischaracterized by including a closed casing, a compression mechanismarranged horizontally within the closed casing for compressing anddischarging a refrigerant, and means for reducing a lateral load appliedto a sliding surface in the compression mechanism, wherein aninflammable refrigerant or a natural refrigerant is used as therefrigerant while no lubricating oil is filled up.

According to the above-described construction, because no lubricatingoil is used, the heat exchanging efficiency in a cooling system isimproved and the efficiency of the whole cooling system is improved.Furthermore, because the refrigerant does not dissolve in thelubricating oil, the amount of refrigerant to be used in the coolingsystem is reduced, and the cost is also reduced. Even if the refrigerantleaks, the possibility of catching fire or exploding is reduced,enhancing the safety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a linear compressor according toa first embodiment of the present invention.

FIG. 2 is a vertical sectional view of a linear compressor according toa second embodiment of the present invention.

FIG. 3 is a vertical sectional view of a linear compressor according toa third embodiment of the present invention.

FIG. 4 is a vertical sectional view of a linear compressor according toa fourth embodiment of the present invention.

FIG. 5 is an enlarged view of an outer peripheral portion of a pistonshown in FIG. 4.

FIG. 6 is a vertical sectional view of a conventional linear compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a linear compressor (vibration type compressor)according to the present invention are discussed hereinafter withreference to the drawings.

Embodiment 1

FIG. 1 depicts a linear compressor according to a first embodiment ofthe present invention, which includes a compression mechanism 1 arrangedvertically within a closed casing 2. The compression mechanism 1includes a motor 3, a cylinder 5, a bearing 6, a piston 8, a cylinderhead 10 and a resonant spring 11, and is elastically supported bysuspension springs (not shown) within the closed casing 2. The motor 3includes a stationary element 4 and a movable element 7 secured to thepiston 8.

The piston 8 is axially slidably supported by the cylinder 5 and thebearing 6. The resonant spring 11 has one end secured to the movableelement 7 of the motor 3 and the other end secured to the bearing 6. 8 adenotes a compression chamber defined by the cylinder 5 and the piston8. A refrigerant gas introduced into the compression chamber 8 a througha suction hole 8 b axially defined in the piston 8 is compressed via areciprocating motion of the piston 8.

The refrigerant compressed by and discharged from the compressionmechanism 1 is an inflammable refrigerant or natural refrigerant such aspropane, isobutane, carbon dioxide or the like. No lubricating oil isfilled up.

In the linear compressor of the above-described construction, the piston8 is driven by the motor 3 to undergo an axial reciprocating motion inthe cylinder 5 and the bearing 6 while receiving an axial elastic forceof the resonant spring 11. Accordingly, only an axial force is appliedto the piston 8 from the motor 3 and the resonant spring 11.Furthermore, a pressure of the gas within the compression chamber 8 aand that of the gas within the closed casing 2 are also applied to endfaces of the piston 8. Such pressures are also axial loads. Because thecompression mechanism 1 is arranged vertically, the weight of the piston8 does not act in a direction perpendicular to the axial direction ofthe piston 8. Because of this, no lateral load is applied to the slidingportions between the piston 8 and the cylinder 5 or the bearing 6 duringthe axial reciprocating motion of the piston 8.

Accordingly, even without any lubricating oil on the sliding portionsbetween the piston 8 and the cylinder 5 or the bearing 6, the compressorcan be operated without causing wear or seizing, while maintaining aslight radial clearance. Because no lubricating oil is used in thecooling system, the heat exchanging efficiency in the cooling system isimproved, and the efficiency of the whole cooling system is improved.

Even if a natural refrigerant or inflammable refrigerant such aspropane, isobutane, carbon dioxide or the like, the use of which ispreferable from the viewpoint of protection of the global environment,is used, the refrigerant never dissolves in a lubricating oil, becauseno lubricating oil is used. Accordingly, the amount of refrigerantrequired for the cooling system can be reduced, compared with a coolingsystem utilizing a lubricating oil, by the amount that dissolves in thelubricating oil. In particular, because hydrocarbons dissolve in thelubricating oil in larger amount than other refrigerants, the amountthereof can be considerably reduced.

Accordingly, the amount of a natural refrigerant or inflammablerefrigerant to be used in the cooling system can be reduced, and thecost can also be reduced. Even if the refrigerant leaks, the possibilityof catching fire or exploding can be reduced.

Moreover, in applications where the use of a vertically arrangedcompressor mechanism is desired in view of the installation space forthe compressor in the cooling system, it is preferred that the linearcompressor according to this embodiment be used.

Embodiment 2

FIG. 2 depicts a linear compressor according to a second embodiment ofthe present invention, in which the compression mechanism 1 isvertically arranged within the closed casing 2, as in the linearcompressor of FIG. 1.

Because the construction of the linear compressor of FIG. 2 is basicallythe same as that of the linear compressor of FIG. 1, only differencestherebetween are discussed hereinafter.

In this embodiment, an elastic member 13 such, for example, as a leafspring is used in place of the bearing 6 and the resonant spring 11,both shown in FIG. 1. An inner peripheral portion of the elastic member13 is connected to the piston 8, while an outer peripheral portion ofthe elastic member 13 is connected to an elastic anchoring member 14mounted on the cylinder 5. By this construction, the piston 8 isradially supported by the elastic member 13 as if it is supported by abearing, and the piston 8 receives an axial elastic force with an axialdisplacement thereof. The piston 8 slides only with respect to thecylinder 5 and, hence, the number of sliding portions is reducedcompared with the first embodiment.

By the above-described construction, the piston 8 is driven by the motor3 to undergo an axial reciprocating motion and slides in the cylinder 5while receiving an axial elastic force of the elastic member 13 actingcounter to the movement thereof. Accordingly, only the axial force isapplied to the piston 8 by the motor 3 and the elastic member 13.

As is the case with the first embodiment, because no lateral load isapplied to the piston 8, even if no lubricating oil exists on thesliding portion between the piston 8 and the cylinder 5, the compressorcan be operated without causing wear or seizing, while maintaining aslight radial clearance. In particular, the sliding portion is presentonly between the piston 8 and the cylinder 5 and, hence, compressoroperation without any lubricating oil can be conducted more easily thanthat in the first embodiment.

Embodiment 3

FIG. 3 depicts a linear compressor according to a third embodiment ofthe present invention, in which the compression mechanism 1 is arrangedhorizontally within the closed casing 2.

Although the linear compressor of FIG. 3 differs in the manner ofinstallation from the linear compressor of FIG. 1, the basicconstruction is the same. Accordingly, only differences are discussedhereinafter.

In this embodiment, a cylinder 15 is provided with means 16 for reducinga lateral load acting thereon at the sliding portion with the piston 8.More specifically, the cylinder 15 has an annular groove 16 a definedtherein at the sliding portion thereof, i.e., an inner surface thereof15 a, and also has a communication passageway 16 b defined therein, oneend of which communicates with a high-pressure portion 10 a within thecylinder head 10 and the other end of which communicates with theannular groove 16 a of the cylinder 15.

In the linear compressor of the above-described construction, the piston8 is driven by the motor 3 to undergo an axial reciprocating motion inthe cylinder 15 and the bearing 6. Accordingly, an axial force isapplied to the piston 8 by the motor 3. Furthermore, because thecompression mechanism 1 is arranged horizontally as in the conventionallinear compressor, the weight of the piston 8 results in a lateral loadacting thereon in a direction perpendicular to the axial direction.

However, a high-pressure refrigerant compressed by the reciprocatingmotion of the piston 8 and discharged into the cylinder head 10 isintroduced into the annular groove 16 a in the inner surface 15 a of thecylinder 15 via the communication an passageway 16 b due to a pressuredifference. That is, the high-pressure refrigerant is discharged intothe slight radial clearance at the sliding portions between the cylinder15 and the piston 8. This high-pressure refrigerant forms an air bearingfor receiving the lateral load 8 on the piston 8.

Accordingly, with the construction in which the compression mechanism 1is arranged horizontally, even if the lateral load is applied to thepiston 8 in a direction perpendicular to the axial direction, the airbearing can considerably reduce the lateral load acting on the slidingportion of the piston 8. Because of this, even if the compressionmechanism 1 is arranged horizontally as in the conventional compressor,and even if no lubricating oil exists on the sliding portions of thepiston 8 and the cylinder 5, the compressor can be operated withoutcausing wear or seizing, while maintaining the slight radial clearance.

Although in this embodiment the cylinder 15 is provided with the airbearing as the means 16 for reducing the lateral load on the slidingportions, the same effect can be obtained even if the air bearing isprovided in the piston 8 or the bearing 6.

In place of the air bearing, the same effect can be obtained byproviding the sliding portions between the piston 8 and the cylinder 15or the bearing 6 with dynamic pressure generating grooves as means forgenerating dynamic pressure upon a reciprocating motion of the piston 8.Any other mechanisms or constructions are applicable if they can reducethe lateral load on the sliding portions of the piston 8.

Furthermore, the lateral load on the sliding portions of the piston 8can also be reduced by reducing the weight of the reciprocating members.For this purpose, the piston 8 may be formed of a material such asaluminum having a small specific gravity, or the weight of the movableelement 7 of the motor 3 may be reduced.

Moreover, in applications where the use of a horizontally arrangedcompressor mechanism is desired in view of the installation space forthe compressor in the cooling system, it is preferred that the linearcompressor according to this embodiment be used.

Embodiment 4

FIG. 4 depicts a linear compressor according to a fourth embodiment ofthe present invention, and FIG. 5 is an enlarged view of a portion A inFIG. 4.

The linear compressor according to this embodiment resembles the linearcompressor according to the second embodiment in the basic construction,but differs in that a piston 17 was surface-treated to have asurface-treated layer 18 formed on a sliding portion thereof usingTeflon™, molybdenum disulfide or alumite.

Even if seizing occurs on the sliding portions due to poor assemblingaccuracy or machining accuracy for the cylinder 5 and the piston 17, oreven if a lateral load is applied to the sliding portions of the piston17 for some reason during operation, the self-lubricating effect of thesurface-treated layer 18 of Teflon™, molybdenum disulfide or alumite canprevent abnormal wear at the sliding portions of the piston 17 and thecylinder 5 even without any lubricating oil.

Also, the surface-treated layer 18 acts to reduce the coefficient offriction with respect to the cylinder 5. As a result, the sliding lossis reduced, enhancing the compressor efficiency.

Although in this embodiment the sliding portion of the piston wassurface-treated, the same effect can be obtained by similarlysurface-treating the sliding portion of the cylinder.

Furthermore, even in the linear compressor according to the first orthird embodiment, the same effect can be obtained by similarlysurface-treating the sliding portions of the piston, cylinder, bearingor the like.

What is claimed is:
 1. A linear compressor comprising: a closed casing;a compression mechanism arranged within said closed casing forcompressing and discharging a refrigerant, said compression mechanismcomprising a cylinder having no lubricating oil located therein, acylinder head mounted on said cylinder, and a piston for compressing therefrigerant, said cylinder head having a high pressure portion intowhich the refrigerant compressed by said piston is discharged, whereinsaid cylinder has a communication passageway defined therein forcommunicating said high pressure portion and contacting surfaces betweensaid cylinder and said piston to reduce a lateral load applied to saidcylinder, wherein one of an inflammable refrigerant and carbon dioxideis used as the refrigerant.
 2. The linear compressor according to claim1, wherein said cylinder has an annular groove defined therein at thesliding portion thereof, and wherein said communication passagewaycommunicates said high pressure portion with said annular groove.
 3. Thelinear compressor according to claim 1, wherein one of the contactingsurfaces of said cylinder and said piston comprises a surface that hasbeen surface-treated using one of polytetrafluoroethylene, molybdenumdisulfide and alumite.
 4. The linear compressor according to claim 1,wherein the inflammable refrigerant comprises propane or isobutane.